How Organisms Obtain EnergyHow Organisms Obtain Energy• One of the most important characteristics of a species’ niche is how it obtains energy.• Ecologists trace the flow of energy through communities to discover nutritional relationships between organisms.

The producers: AutotrophsThe producers: Autotrophs

• Other organisms in the biosphere depend on autotrophs for nutrients and energy. These dependent organisms are called consumers.

• autotroph (producer) - An organism that uses light energy to make energy-rich compounds

The producers: AutotrophsThe producers: Autotrophs• The ultimate source of the energy for life is the sun.

• Plants use the sun’s energy to manufacture food in a process called photosynthesis.

The consumers: HeterotrophsThe consumers: Heterotrophs

• Heterotrophs include organisms that feed only on autotrophs, organisms that feed only on other heterotrophs, and organisms that feed on both autotrophs and heterotrophs.

• Heterotroph - An organism that cannot make its own food and feeds on other organisms

The consumers: Herbivores - plant eatersThe consumers: Herbivores - plant eaters

• Herbivore - A heterotroph that feeds only on plants

• Heterotrophs display a variety of feeding relationships.

The consumers: Carnivores - flesh eatersThe consumers: Carnivores - flesh eaters

• Some heterotrophs eat other heterotrophs

• Carnivores - Animals that kill and eat only other animals

The consumers: OmnivoresThe consumers: Omnivores• Ominvores eat both plants & animals

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The consumers: DecomposersThe consumers: Decomposers

• Decomposers break down the complex compounds of dead and decaying plants and animals into simpler molecules that can be more easily absorbed.

The consumers: DecomposersThe consumers: Decomposers• Some organisms, such as bacteria and fungi, are decomposers.

Flow of Matter & Energy in Ecosystems

Matter, in the form of carbon, nitrogen, and other elements is

recycled in an ecosystem.

Energy is not recycled because every time energy is transferred, some is “lost” to the environment as heat.

Cycles in NatureCycles in Nature

• Matter, in the form of nutrients, moves through, or is part of, all organisms at each trophic level.

• But matter is cycled and is not replenished like the energy from sunlight. There is a finite amount of matter.

Pathways for matter and energyPathways for matter and energy

• In a food chain, nutrients and energy move from autotrophs to heterotrophs and, eventually, to decomposers.

• Food chain - a simple model that shows how matter and energy move through an ecosystem.

Food chains: Pathways for matter and energyFood chains: Pathways for matter and energy

• A food chain is drawn using arrows to indicate the direction in which energy is transferred from one organism to the next.berries → mice → black bear

Trophic levels represent links in the chainTrophic levels represent links in the chain

• Each organism in a food chain represents a feeding step, or trophic level, in the passage of energy and materials.

• A first order consumer is an organism that feeds on plants, such as a grasshopper.

Trophic levels represent links in the chainTrophic levels represent links in the chain

• A second order consumer is an organism that feeds on a first order consumer.

• A food chain represents only one possible route for the transfer of matter and energy through an ecosystem.

Food Chains

•Simple food chains are often unstable because each organism feeds on only one thing. If one population is wiped out, the entire chain collapses

Food chains: Pathways for matter and energyFood chains: Pathways for matter and energy• Most food chains consist of two, three, or four transfers.

• The amount of energy remaining in the final transfer is only a portion of what was available at the first transfer.

• A portion of the energy is given off as heat at each transfer.

Food Web

Food web - a model that shows all the possible feeding relationships at each trophic level in a community.It is a complex feeding relationship consisting of interconnected food chains.

Food Web

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Ecological pyramidsEcological pyramids

• An ecological pyramid can show how energy flows through an ecosystem.

• The base of the ecological pyramid represents the autotrophs, or first trophic level. Higher trophic levels are layered on top of one another.

Energy and trophic levels: Ecological pyramidsEnergy and trophic levels: Ecological pyramids

• The pyramid of energy illustrates that the amount of available energy decreases at each succeeding trophic level.

Pyramid of Energy

Heat

Heat

Heat

Heat

0.1% Consumers

1% Consumers

10% Consumers

100% Producer

s

Parasites,

scavengers, and

decomposers feed at

each level.

Energy and trophic levels: Ecological pyramidsEnergy and trophic levels: Ecological pyramids

• The amount of useable energy decreases from one trophic level to the next; it is lost as 1. Heat and 2. Waste

Pyramid of Energy

Heat

Heat

Heat

Heat

0.1% Consumers

1% Consumers

10% Consumers

100% Producer

s

Parasites,

scavengers, and

decomposers feed at

each level.

The 10% Rule• Only ten percent of the energy available in a trophic level is retained by the consumer; ninety percent is lost.

• This is because organisms fail to capture and eat all the food energy available at the trophic level below them.

Energy and trophic levels: Ecological pyramidsEnergy and trophic levels: Ecological pyramids

• A pyramid of numbers shows that population sizes decrease at each higher trophic level.

Pyramid of Numbers

Fox (1)

Birds (25)

Grasshoppers (250)

Grasses (3000)

Energy and trophic levels: Ecological pyramidsEnergy and trophic levels: Ecological pyramids

• An ecosystem has a limited number of large carnivores due to food availability.

Pyramid of Numbers

Fox (1)

Birds (25)

Grasshoppers (250)

Grasses (3000)

Energy and trophic levels: Ecological pyramidsEnergy and trophic levels: Ecological pyramids

• A pyramid of numbers may be inverted if for example, one tree is the food source for thousands of insects.

Pyramid of Numbers

Fox (1)

Birds (25)

Grasshoppers (250)

Grasses (3000)

Energy and trophic levels: Ecological pyramidsEnergy and trophic levels: Ecological pyramids• Biomass is the total weight of living matter at each trophic level. A pyramid of biomass represents the total weight of living material available at each trophic level.

Pyramid of Biomass

1 kilogram of human tissue10 kilograms of beef

100 kilograms of grain